This invention relates to scanning nonplanar originals, such as bound books or other three dimensional objects.
Input scanners are widely used for producing digital versions of images on substrates. Digital versions are beneficial because they can be stored, processed, transmitted, and subsequently used by other devices, such as computers, copiers, and facsimile machines.
Input scanners usually include a flat, transparent platen that supports a substrate having an image that is to be digitized, and a moving raster scanner having a light source that radiates a narrow xe2x80x9cscan linexe2x80x9d of light through the platen and onto the substrate. Part of that light is reflected by the image on the substrate and collected and focused by the raster scanner""s input optics onto an elongated light sensor array. The light sensor then converts its received light into digital signals that are then stored. As the raster scanner moves across the substrate the scan line of light sweeps over the substrate and other scan lines are digitized. When the substrate""s image has been completely scanned the digital signals of all of the scan lines represent a digital version of the image.
Scanning three-dimensional (non-planar) substrates such as bound books presents problems. One set of problems relates to keeping the object plane of the light into the sensor array on the three-dimensional object as the raster scanner moves. For example, when scanning a book the book""s pages near the binding tends to become defocused as the pages lift off the platen. Even relatively minor variations between a three-dimensional object and the object plane can cause serious problems. For example, some input scanners that use gradient index lens arrays can become significantly defocused by a separation of as little as 1 millimeter.
Various approaches have been taken in the prior art to reduce the problems related to scanning three-dimensional objects. With books, one approach is to use xe2x80x9cbrute forcexe2x80x9d to press the book against the platen, thereby reducing the book""s lift. However, portions of the book""s pages still remain above the platen""s surface. Moreover, pressing a book against a flat platen can degrade the book""s binding, especially with older books. Another approach is to use a wedged platen to reduce binding degradation. However, wedged platens tend to reduce overall machine utility and increase cost.
Other approaches are described in U.S. Pat. No. 5,276,530, which issued on Jan. 4, 1994, and which is entitled xe2x80x9cDocument reproduction machine with electronically enhanced book copying capability.xe2x80x9d That patent mentions a reproduction machine having a height sensor on a scanner that determines the distance between a reference point (which may be in the object plane) and the original being scanned. The height information is used to control the position of a scanning mirror that adjusts the focus, illumination, and scan rate. Furthermore, U.S. Pat. No. 5,276,530 teaches using information from a height sensor as an input to an electronic correction circuit that electronically corrects for defocusing caused by height variations. However, the incorporation of a height sensor adds cost and complexity. Therefore, a new approach to copying three-dimensional objects on a flat platen would be beneficial.
The principles of the present invention provide for improved scanning of a three-dimensional object placed on a platen. An input scanner according to the principles of the present invention includes a platen for locating a three-dimensional object that is to be scanned, a contoured track guide adjacent the platen, and a moving raster scanner that moves along the track guide and across the platen. The raster scanner includes a light source that produces a scan line of light, an elongated light sensor array for digitizing received light, and input optics that focuses light reflected from an object plane onto the light sensor array. The raster scanner produces a digital representation of a line image having an object plane that is a fixed distance in front of the raster scanner""s input optics. The contour of the track guide adjusts the spatial position of the raster scanner, and thus the spatial position of the object plane, in the Z-direction as the raster scanner moves such that the three-dimensional object tends to remain in focus. Beneficially, the track guide is a feature of the platen itself.
If the three-dimensional object being scanned is a book, the contour of the track guide is such that it approximates the contour of the book""s binding.